Buggy code:
public static String join ( Iterable < ? > iterable , char separator ) { } public static String join ( Iterable < ? > iterable , String separator ) { } public static String deleteWhitespace ( String str ) { } public static String removeStart ( String str , String remove ) { } public static String removeStartIgnoreCase ( String str , String remove ) { } public static String removeEnd ( String str , String remove ) { } public static String removeEndIgnoreCase ( String str , String remove ) { } public static String remove ( String str , String remove ) { } public static String remove ( String str , char remove ) { } public static String replaceOnce ( String text , String searchString , String replacement ) { } public static String replace ( String text , String searchString , String replacement ) { } public static String replace ( String text , String searchString , String replacement , int max ) { } public static String replaceEach ( String text , String [ ] searchList , String [ ] replacementList ) { } public static String replaceEachRepeatedly ( String text , String [ ] searchList , String [ ] replacementList ) { } private static String replaceEach ( String text , String [ ] searchList , String [ ] replacementList , boolean repeat , int timeToLive ) { } public static String replaceChars ( String str , char searchChar , char replaceChar ) { } public static String replaceChars ( String str , String searchChars , String replaceChars ) { } public static String overlay ( String str , String overlay , int start , int end ) { } public static String chomp ( String str ) { } public static String chomp ( String str , String separator ) { } public static String chop ( String str ) { } public static String repeat ( String str , int repeat ) { } public static String repeat ( String str , String separator , int repeat ) { } private static String padding ( int repeat , char padChar ) throws IndexOutOfBoundsException { } public static String rightPad ( String str , int size ) { } public static String rightPad ( String str , int size , char padChar ) { } public static String rightPad ( String str , int size , String padStr ) { } public static String leftPad ( String str , int size ) { } public static String leftPad ( String str , int size , char padChar ) { } public static String leftPad ( String str , int size , String padStr ) { } public static int length ( CharSequence cs ) { } public static String center ( String str , int size ) { } public static String center ( String str , int size , char padChar ) { } public static String center ( String str , int size , String padStr ) { } public static String upperCase ( String str ) { } public static String upperCase ( String str , Locale locale ) { } public static String lowerCase ( String str ) { } public static String lowerCase ( String str , Locale locale ) { } public static String capitalize ( CharSequence cs ) { } public static String uncapitalize ( CharSequence cs ) { } public static String swapCase ( String str ) { } public static int countMatches ( String str , String sub ) { } public static boolean isAlpha ( CharSequence cs ) { } public static boolean isAlphaSpace ( CharSequence cs ) { } public static boolean isAlphanumeric ( CharSequence cs ) { } public static boolean isAlphanumericSpace ( CharSequence cs ) { } public static boolean isAsciiPrintable ( CharSequence cs ) { } public static boolean isNumeric ( CharSequence cs ) { } public static boolean isNumericSpace ( CharSequence cs ) { } public static boolean isWhitespace ( CharSequence cs ) { } public static boolean isAllLowerCase ( CharSequence cs ) { } public static boolean isAllUpperCase ( CharSequence cs ) { } public static String defaultString ( String str ) { } public static String defaultString ( String str , String defaultStr ) { } public static < T extends CharSequence > T defaultIfEmpty ( T str , T defaultStr ) { } public static String reverse ( String str ) { if ( str == null ) { return null ; } <START_BUG> return CharSequenceUtils . reverse ( str ) . toString ( ) ; <END_BUG> } public static String reverseDelimited ( String str , char separatorChar ) { } public static String abbreviate ( String str , int maxWidth ) { } public static String abbreviate ( String str , int offset , int maxWidth ) { } public static String abbreviateMiddle ( String str , String middle , int length ) { } public static String difference ( String str1 , String str2 ) { } public static int indexOfDifference ( CharSequence cs1 , CharSequence cs2 ) { } public static int indexOfDifference ( CharSequence [ ] css ) { } public static String getCommonPrefix ( String [ ] strs ) { } public static int getLevenshteinDistance ( CharSequence s , CharSequence t ) { } public static boolean startsWith ( String str , String prefix ) { } public static boolean startsWithIgnoreCase ( String str , String prefix ) { } private static boolean startsWith ( String str , String prefix , boolean ignoreCase ) { } public static boolean startsWithAny ( String string , String [ ] searchStrings ) { } public static boolean endsWith ( String str , String suffix ) { } public static boolean endsWithIgnoreCase ( String str , String suffix ) { } private static boolean endsWith ( String str , String suffix , boolean ignoreCase ) { } }

Fix:
return new StringBuilder ( str ) . reverse ( ) . toString ( ) ;